This section provides background information related to the present disclosure which is not necessarily prior art. In the past, it has been known that a core structure of a heat exchanger 5 comprises of a plurality of tubes 7 through the inside of which an internal heat exchange medium passes, a plurality of fins alternately stacked with the tubes 7 and increasing the heat transfer of said heat exchange medium, end tanks 6 to which the two ends of the tubes are connected, and side plates 10 arranged at the outsides in the stacking direction from the end fins arranged at the outermost sides in the stacking direction of the fins and connected to the end tanks 6 (see FIG. 1).
In this types of core structure of a heat exchanger, the tubes and the corrugated fins are alternately arranged between the two end tanks arranged facing each other across a predetermined distance. The two ends of the two end tanks are bridged by the side plates 10. Further, the two ends of the tubes 7 and the side plates 10 are inserted into tube holes located in core plates (not shown) of the end tanks 6 and subsequently brazed.
However, in the aforementioned heat exchanger, when the heat exchange medium begins to pass through the tubes 7, the difference between the amount of heat expansion of the tubes 7 and the core plates which directly receive the effect of the heat exchange medium and the amount of heat expansion of the side plates 10 which do not directly receive the effect of the heat exchange medium causes thermal stress accompanied with thermal strain in the tubes 7 and the side plates 10. Further, if thermal stress is repeatedly generated, there is the problem of fatigue breakage in the vicinities of the tube and core plate interface.
As a countermeasure, there is the art described in U.S. Pat. No. 7,198,095. In this patent, there is a thermal expansion ‘break-off zone’ provided on the side plates. This design enables a predetermined breaking point, adapted to break when subjected to thermally-induced stress caused in the tubes during operation of the heat exchanger.
However, in this design, the complete breakage of the side plate provides a location for buckling of the corrugated fins and tubes adjacent to the side plates, creating a dimensional error of the core unit assembly.
U.S. Pat. No. 7,389,810 improves on this, by providing a flexible zone to accommodate thermal expansion, but further requires a cutting process of the base portion during manufacturing, which must be accomplished prior to assembly of the heat exchanger. This cutting step makes post assembly alignment and brazing difficult.